The present invention relates to a variable displacement compressor used in a refrigerant circuit of a vehicle air-conditioner.
In a variable displacement compressor, a cylinder bore is formed in a housing and a drive shaft is rotatably supported in the housing. A lug plate is connected to the drive shaft so as to rotate therewith, and a swash plate is supported on the drive shaft so as to incline with respect to the drive shaft. A link mechanism is arranged between the lug plate and the swash plate. A piston is accommodated in the cylinder bore for reciprocation and is engaged with the outer periphery of the swash plate.
The drive shaft is rotationally driven by a vehicle engine. The rotation of the drive shaft is transmitted to the swash plate through the lug plate and the link mechanism, so that the piston is reciprocated to compress refrigerant gas. The inclination angle of the swash plate is varied while the swash plate is guided by the link mechanism so that the stroke of the piston is changed and the displacement of the compressor is varied.
Japanese Patent Application Publication No. 2001-289159 discloses a link mechanism. As shown in FIG. 8, the link mechanism includes a link pin 103 and first and second brackets 104 fixed to a swash plate 101 and a lug plate 102, respectively. The link pin 103 has at its end first and second spherical portions 103a and 103b which are formed rearward and forward with respect to a rotational direction R of the drive shaft, respectively, or the right and left sides as seen in FIG. 8. The first and second brackets 104 have their respective first and second guide grooves 102a and 102b formed at their end faces facing to the link pin 103. The first and second grooves 102a and 102b receive and guide the corresponding spherical portions 103a and 103b. 
The rotation of the lug plate 102 is transmitted from the lug plate 102 to the swash plate 101 through the inner surface of the first guide groove 102a and the spherical surface of the first spherical portion 103a. Compression reactive force is eccentrically applied to the swash plate 101 through the piston, and its load center is indicated by the arrow X in FIG. 8. The compression reactive force from the second spherical portion 103b is mainly received by the inner surface of the second guide groove 102b. The swash plate 101 in varying its inclination angle is guided in such a manner that the first and second spherical portions 103a, 103b slide over the respective inner surfaces of the first and second guide grooves 102a, 102b. 
Here, the rotation of the lug plate 102 is not transmitted to the swash plate 101 through the second guide groove 102b since the second guide groove 102b is located on the preceding side of the rotational direction R with respect to the second spherical portion 103b. And also, the inner surface area of the second guide groove 102b that faces to the swash plate 101 receives the compression reactive force but other surface area does not. Accordingly, a wall portion 104a of the second bracket 104 is relevant to neither transmitting the lug plate rotation to the swash plate 101 nor transmitting the compression reactive force X from the swash plate 101 to the lug plate 102. The wall portion 104a of the second bracket 104 functions to restrict the swash plate 101 from further rotating toward the preceding side of the rotational direction R relative to the lug plate 102 when the second spherical portion 103b comes into contact with the inner surface of the second guide groove 102b. If the wall portion 104a of the second bracket 104 is simply removed, the swash plate 101 would substantially wobble forward and backward of the rotational direction R relative to the lug plate 102. Namely, when the swash plate 101 substantially wobbles forward and backward of the rotational direction R, the first spherical portion 103a repeatedly and fiercely collides with the inner surface of the first guide groove 102a, so that the variable displacement compressor generates abnormal noise and vibration.
Meanwhile, when the wall portion 104 of the second bracket 104 is provided, since the wall portion 104a has to have certain thickness, the interval between the first and second spherical portions 103a, 103b and the interval between the first and second guide grooves 102a, 102b has to be narrow by the thickness of the wall portion 104a. When the interval between the first and second spherical portions 103a, 103b and the interval between the first and second guide grooves 102a, 102b are narrow, the support of the swash plate 101 by the lug plate 102 is unstable under the compression reactive force X which is eccentrically applied to the radially outer portion of the swash plate 101. The eccentrically applied compression reactive force X makes the swash plate 101 incline in a direction different from its inclining direction when the displacement is varied. Due to this differently inclining swash plate 101, the first and second spherical portions 103a, 103b contact the respective first and second guide grooves 102a, 102b in different manners, so that sliding resistance between them becomes large. Thus, controllability of the displacement of the variable displacement compressor deteriorates.
The present invention is directed to a variable displacement compressor having a link mechanism that prevents a cam plate from substantially wobbling forward and backward along the rotational direction and being inclined in a direction different from its inclining direction when the displacement is varied.